Nature Watch
January 28, 2009
By Susan Benson,CNHM Director of Education
“Wind chill advisories” and “below zero temperatures;” these are phrases we have become quite familiar with as regular parts of our vocabulary this winter. Throughout all of these cold nights, I’ve been interested by the fog we’ve woken up to on and off in the past few weeks, and I had to look further for more information.
I first looked to recent weather forecasts to find some mention of fog, and was surprised to discover ice fog, a phenomena I was unfamiliar with. Ice fog, perhaps something that happens less often in northern Wisconsin, has been in forecasts in the past few weeks. In mid-December ice fog shrouded Big Bay State Park as arctic air met warmer Lake Superior waters, and ski trails are still impassable yet today as a result of this event. An event that arctic regions are more familiar with, ice fog can occur during long, cold nights, as the snow-covered ground radiates heat to space, and air temperatures at the surface become increasingly colder. Ice fog occurs when water droplets have frozen into tiny crystals of ice in midair. Usually, this occurs when temperatures are at or below -30 degrees Fahrenheit.
During clear night skies, incoming solar radiation is greatly reduced, and the snow surface loses more energy than it gains. Because of this energy loss, the snow surface gets colder, cooling the air in contact with it, and making a colder layer of air that develops over the snowpack. This condition is called a temperature inversion because it is opposite of normal conditions when the air close to the ground is warmer than the air above it. When calm air is present at night, this inversion can develop and become cooler, sometimes going even several hundred meters above the ground surface, and creating conditions for ice fog.
Ice fog can also occur in urban areas due to water vapor present in automobile exhaust fumes or smokestack emissions. Normally these pollutants would rise into the atmosphere because they are warmer and lighter than the air into which they are emitted, but when conditions are right, these strong temperature inversions cause the polluted air to become trapped at ground level, resulting in the formation of ice fog.
Some of us might be feeling cabin fever as these cold temperatures and wind chills keep us feeling stuck more often indoors, but there are still interesting events that can be learned about and experienced here in the north woods. If you find these winter blues keep you indoors, perhaps you will find your way to your local library to read more about the life here in the cold, enjoy winter views through the windows of your warm home, or just dress for success in many warm layers for your outdoor excursions.
Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M or on the web at http://www.cablemuseum.org/ to learn more about exhibits and programs.
Wednesday, January 28, 2009
Wednesday, January 21, 2009
Subnivean Temperatures
Nature Watch
January 21, 2009
By Susan Benson,CNHM Director of Education
The subnivean space – perhaps it sounds like something out of a science fiction novel, something you might find on a journey to the center of the earth. However, it is not as mystifying as one might think. Quite simply, the subnivean space is the layer between the ground and snowpack. While the snow cover builds up, the ground gives off heat, creating water vapor that condenses and freezes under the bottom layer of snow, creating small spaces at ground level. Many small animals would never survive the winter cold without this space.
The minute a snowflake falls, it begins changing its shape. It can be affected by the internal snowpack characteristics and the external weather conditions. The first deterioration of a snowflake begins as a “destructive” change, in which the snow grains become more rounded. The unequal temperature distribution in the snowpack causes the water molecules to melt, changing the radiating arms of the snowflakes into a rough, spherical ice particle. These ice grains can then connect together, until they are roughly the same size. This metamorphosis occurs more quickly when air temperature is warmer, and is also influenced by wind or the weight of the snow above. It is this destructive metamorphosis that makes building snow shelters so effective.
The snowpack also is exposed to constructive metamorphosis, a process in which the temperature changes from the bottom to top of the snowpack is significantly different. The snow’s upper part is affected by the air temperature, and the lower part is warmed by the ground. Heat is conducted very slowly upward through the snow, affecting the water vapor distribution, and creating a 100% relative humidity in many of the air spaces in the snow. This process causes the ice crystals at the bottom of the snowpack to get continually smaller. Eventually, they form “depth hoar,” brittle, loosely arranged crystals that create easy movement for small mammals as they search for food under the winter snow.
The third factor which affects snow is the “melt metamorphosis”, in which happens when the snowpack is impacted by above freezing temperatures. Surface snow melt percolates down through the snowpack, encounters lower temperatures, and refreezes. As it freezes, it releases heat, bringing the entire snowpack to a more equal temperature. Rain and fog can also cause a similar effect.
Doesn’t the sun’s solar radiation warm the snowpack as well? We all know that spending a day in the snow in bright sunlight is shocking to our eyes, because snow is highly reflective of incoming solar radiation. Perhaps better than a mirror, snow reflects 75-95% of the sunlight hitting its surface. This means that a small amount of solar energy is available to raise the temperature of the snow. However, aging snow, as it accumulates dust, can decrease the sun’s reflection to as low as 45 percent.
It is easy to see that although complex processes occur, the snowpack provides amazing insulation for the winter survival of organisms. How much snow is enough? One theory is that 20 centimeters is a critical depth. The subnivean layer and its temperature and effectiveness for animal survival can also be affected by the type of snowpack metamorphosis that has occurred. By the time the snowpack reaches 40-50 centimeters, the subnivean environment temperature is almost constant.
Most importantly to our animal world, it is as if the snow peels away from the ground, leaving pockets where mice, voles, and shrews spend the winter. Some predators such as weasels live there too. Under that white snow in your yard there is an entire food chain still at work! Next time you are out for a ski, hike, or on a snowmobile trail, look at the edges of the trails to see if you can observe tunnels created by animals living in the snow.
Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M or on the web at www.cablemuseum.org to learn more about exhibits and programs.
January 21, 2009
By Susan Benson,CNHM Director of Education
The subnivean space – perhaps it sounds like something out of a science fiction novel, something you might find on a journey to the center of the earth. However, it is not as mystifying as one might think. Quite simply, the subnivean space is the layer between the ground and snowpack. While the snow cover builds up, the ground gives off heat, creating water vapor that condenses and freezes under the bottom layer of snow, creating small spaces at ground level. Many small animals would never survive the winter cold without this space.
The minute a snowflake falls, it begins changing its shape. It can be affected by the internal snowpack characteristics and the external weather conditions. The first deterioration of a snowflake begins as a “destructive” change, in which the snow grains become more rounded. The unequal temperature distribution in the snowpack causes the water molecules to melt, changing the radiating arms of the snowflakes into a rough, spherical ice particle. These ice grains can then connect together, until they are roughly the same size. This metamorphosis occurs more quickly when air temperature is warmer, and is also influenced by wind or the weight of the snow above. It is this destructive metamorphosis that makes building snow shelters so effective.
The snowpack also is exposed to constructive metamorphosis, a process in which the temperature changes from the bottom to top of the snowpack is significantly different. The snow’s upper part is affected by the air temperature, and the lower part is warmed by the ground. Heat is conducted very slowly upward through the snow, affecting the water vapor distribution, and creating a 100% relative humidity in many of the air spaces in the snow. This process causes the ice crystals at the bottom of the snowpack to get continually smaller. Eventually, they form “depth hoar,” brittle, loosely arranged crystals that create easy movement for small mammals as they search for food under the winter snow.
The third factor which affects snow is the “melt metamorphosis”, in which happens when the snowpack is impacted by above freezing temperatures. Surface snow melt percolates down through the snowpack, encounters lower temperatures, and refreezes. As it freezes, it releases heat, bringing the entire snowpack to a more equal temperature. Rain and fog can also cause a similar effect.
Doesn’t the sun’s solar radiation warm the snowpack as well? We all know that spending a day in the snow in bright sunlight is shocking to our eyes, because snow is highly reflective of incoming solar radiation. Perhaps better than a mirror, snow reflects 75-95% of the sunlight hitting its surface. This means that a small amount of solar energy is available to raise the temperature of the snow. However, aging snow, as it accumulates dust, can decrease the sun’s reflection to as low as 45 percent.
It is easy to see that although complex processes occur, the snowpack provides amazing insulation for the winter survival of organisms. How much snow is enough? One theory is that 20 centimeters is a critical depth. The subnivean layer and its temperature and effectiveness for animal survival can also be affected by the type of snowpack metamorphosis that has occurred. By the time the snowpack reaches 40-50 centimeters, the subnivean environment temperature is almost constant.
Most importantly to our animal world, it is as if the snow peels away from the ground, leaving pockets where mice, voles, and shrews spend the winter. Some predators such as weasels live there too. Under that white snow in your yard there is an entire food chain still at work! Next time you are out for a ski, hike, or on a snowmobile trail, look at the edges of the trails to see if you can observe tunnels created by animals living in the snow.
Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M or on the web at www.cablemuseum.org to learn more about exhibits and programs.
Wednesday, January 14, 2009
Irruption of Redpolls
Nature Watch
January 14, 2009
By Susan Benson,CNHM Director of Education
Do you have a larger number of pine siskins or redpolls at your feeder this winter? Have you seen siskins or crossbills in flocks along the roadsides? After checking with some local birders, it appears that siskins are present in area feeders, although less redpolls this winter. Crossbills are being seen along the roadsides, and sometimes are casualties as they don’t quite make it out of the way of cars. Irruptions, the seasonal movement of winter birds to our backyards happens with more than the owls I mentioned the past two weeks.
An irruption is comparable to bird migration, but it takes place more irregularly, usually every two to four years, depending on the species, rather than every year. Most irruptions result because of food shortages in areas where some bird species usually spend their winters. When they cannot find sufficient food, these birds move south in larger numbers. In many bird species, small numbers move south every winter, but irruptions are noticeable through their great abundance of the species south of its usual range. During winters when seed crops, especially of deciduous trees, are poor in the north, food is scarce for seed-eating species. This occurrence adds a dramatic level of excitement to winter birding. Some of the birds we are most likely to see in these winter irruptions are the winter finches such as common redpolls, pine siskins, pine grosbeaks, red crossbills, white-winged crossbills, purple finches, and evening grosbeaks. Other species shift their typical winter grounds on occasion, such as the bohemian waxwing, varied thrush, red-breasted nuthatch, or the Clark’s nutcracker. When many species irrupt during the same year, it is called a "superflight."
The common redpoll, named for the red cap on its head, is a regular irruptive species that usually comes south into our area every few years. Redpolls feed primarily on the catkins of birch and alder trees in their wintering grounds. In a year of poor catkin production, redpolls will move south, frequenting our bird feeders for seed foods. Redpolls love thistle, or nyger seed, and will swarm thistle feeders in large numbers. On irruptive years, feeder flocks can reach 40 or 50, and upwards towards 100 birds. Redpolls have throat pouches for temporarily storing seeds, so when at feeders they may fill their pouches with seeds quickly, and fly to a more protected area to eat the seeds. During mid-March, redpolls will begin their journey north again.
Red and white-winged crossbills are two irruptive species that depend so completely on conifer seeds for food that they regularly wander far and wide during winter. They are the only birds in North America that have bills crossing at the tips like confused scissors. One story is that the bill shape arose because crossbills tried to extract nails that held Jesus to the cross, but biologists explain that it enables birds to pry apart cone scales for seed extraction with their spoon-tipped tongues. They can also hold cones with their legs, and hang upside down, using their bills to cling to branches – making them seem a bit like a northern parrot-like bird. Since cone-bearing trees are unreliable in their cone crop, this makes crossbills more nomadic and unpredictable. Certainly, with the pine cone crop we saw fall this year, it is not a surprise to be seeing or hearing about crossbills in the area this winter. This morning, Museum staff observed flocks of probably over 250 crossbills in the conifers around the Museum.
Scientists at the Cornell Lab of Ornithology are studying why these irruptions occur, and are monitoring these events. Citizens can find an online bird irruption survey form to submit on their BirdSource website. Although we might not be experiencing a “superflight” year, keep an eye out at your feeder, or along roadsides for any of those fun-to-see irruptive bird species.
An added note of caution: Please watch for flocks of birds resting on our local highways during the extreme cold. They are ingesting gravel which helps with their digestive system. They are slow to move and we have been noting many casualties.
Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M or on the web at http://www.cablemuseum.org/ to learn more about exhibits and programs.
January 14, 2009
By Susan Benson,CNHM Director of Education
Do you have a larger number of pine siskins or redpolls at your feeder this winter? Have you seen siskins or crossbills in flocks along the roadsides? After checking with some local birders, it appears that siskins are present in area feeders, although less redpolls this winter. Crossbills are being seen along the roadsides, and sometimes are casualties as they don’t quite make it out of the way of cars. Irruptions, the seasonal movement of winter birds to our backyards happens with more than the owls I mentioned the past two weeks.
An irruption is comparable to bird migration, but it takes place more irregularly, usually every two to four years, depending on the species, rather than every year. Most irruptions result because of food shortages in areas where some bird species usually spend their winters. When they cannot find sufficient food, these birds move south in larger numbers. In many bird species, small numbers move south every winter, but irruptions are noticeable through their great abundance of the species south of its usual range. During winters when seed crops, especially of deciduous trees, are poor in the north, food is scarce for seed-eating species. This occurrence adds a dramatic level of excitement to winter birding. Some of the birds we are most likely to see in these winter irruptions are the winter finches such as common redpolls, pine siskins, pine grosbeaks, red crossbills, white-winged crossbills, purple finches, and evening grosbeaks. Other species shift their typical winter grounds on occasion, such as the bohemian waxwing, varied thrush, red-breasted nuthatch, or the Clark’s nutcracker. When many species irrupt during the same year, it is called a "superflight."
The common redpoll, named for the red cap on its head, is a regular irruptive species that usually comes south into our area every few years. Redpolls feed primarily on the catkins of birch and alder trees in their wintering grounds. In a year of poor catkin production, redpolls will move south, frequenting our bird feeders for seed foods. Redpolls love thistle, or nyger seed, and will swarm thistle feeders in large numbers. On irruptive years, feeder flocks can reach 40 or 50, and upwards towards 100 birds. Redpolls have throat pouches for temporarily storing seeds, so when at feeders they may fill their pouches with seeds quickly, and fly to a more protected area to eat the seeds. During mid-March, redpolls will begin their journey north again.
Red and white-winged crossbills are two irruptive species that depend so completely on conifer seeds for food that they regularly wander far and wide during winter. They are the only birds in North America that have bills crossing at the tips like confused scissors. One story is that the bill shape arose because crossbills tried to extract nails that held Jesus to the cross, but biologists explain that it enables birds to pry apart cone scales for seed extraction with their spoon-tipped tongues. They can also hold cones with their legs, and hang upside down, using their bills to cling to branches – making them seem a bit like a northern parrot-like bird. Since cone-bearing trees are unreliable in their cone crop, this makes crossbills more nomadic and unpredictable. Certainly, with the pine cone crop we saw fall this year, it is not a surprise to be seeing or hearing about crossbills in the area this winter. This morning, Museum staff observed flocks of probably over 250 crossbills in the conifers around the Museum.
Scientists at the Cornell Lab of Ornithology are studying why these irruptions occur, and are monitoring these events. Citizens can find an online bird irruption survey form to submit on their BirdSource website. Although we might not be experiencing a “superflight” year, keep an eye out at your feeder, or along roadsides for any of those fun-to-see irruptive bird species.
An added note of caution: Please watch for flocks of birds resting on our local highways during the extreme cold. They are ingesting gravel which helps with their digestive system. They are slow to move and we have been noting many casualties.
Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M or on the web at http://www.cablemuseum.org/ to learn more about exhibits and programs.
Wednesday, January 7, 2009
Other Bird Irruptions
Nature Watch
January 7, 2009
By Susan Benson,
CNHM Director of Education
If I mention a snowy owl, Harry Potter’s Hedwig might be one thought some readers may think about. For a naturalist, though, seeing any owl is a prize. Snowy owls might be one of the most spectacular species that flies south during an irruption year, when the prey population appears to decline. Boreal owls, northern hawk owls, and great gray owls move southward during some winters as well.
The boreal owl ranks as one of North America’s most wanted bird species on many birders’ lists. The challenge in finding this bird is all about location, location, location. Boreal owls prefer conifer or mixed-conifer forests in an old growth northern habitat. This bird becomes even more difficult to find since it roosts in dense spruce or balsam fir conifers, five to twenty feet high, usually on a branch next to the trunk. Boreal owls are not true migrants but are irruptive in nature, with most studies showing a four to five year irruption cycle. The year 2004 was its last irruption year, with over 300 boreal owls banded on the north shore of Lake Superior in Minnesota. Small rodents such as mice and voles make up 90-98% of its diet, with insects or small birds making up for the remaining food intake. Normally a nocturnal hunter, it will also hunt during cloudy daylight hours, sitting and waiting for its prey located mostly through its hearing.
The first and only time I have observed a northern hawk owl was in the winter of 2005 at the Ashland airport, where it was spending its days on power lines or telephone poles for days before I got my first glimpse. These birds are also nomadic, wandering south of their normal northern boreal forests, again during years of high reproduction followed by low prey availability. Hawk owls are mostly diurnal (active during daylight hours,) hunting for small mammals or birds from tree top perches. These birds have also been observed caching their prey, stashing it in tree limbs for later consumption.
In the area’s snow covered fields, perched atop a telephone pole, a great gray owl can sometimes be observed. This bird’s irruptions, also believed to be related to prey availability, are perhaps more sporadic. Some great grays can be seen in our area during any winter. In Manitoba, some individuals have migrated up to 700 kilometers, compared to only 43 kilometers in Oregon. In the recent irruption year of 2004-05, over 2,000 great grays were observed in northern Minnesota, an amazing occurrence compared to the normal winter bird count of 35 of this species. One of the world’s largest owls, this bird’s five feet wingspan is an amazing sight. Its main source of food is voles and other small rodents.
Some phenologists or birders will drive great lengths to see some of these birds. If you find you are one of them, the best viewing times for great gray or northern hawk owls appear to be first thing in the morning or late afternoon. Overcast or foggy weather makes for good viewing all day. When searching, focus on tree-tops for northern hawk owls, or about eye level in areas with lots of conifers for great grays. Quality observations of these owls can happen from your vehicle, making hiking into bogs or other areas less necessary.
Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M or on the web at www.cablemuseum.org to learn more about exhibits and programs.
January 7, 2009
By Susan Benson,
CNHM Director of Education
If I mention a snowy owl, Harry Potter’s Hedwig might be one thought some readers may think about. For a naturalist, though, seeing any owl is a prize. Snowy owls might be one of the most spectacular species that flies south during an irruption year, when the prey population appears to decline. Boreal owls, northern hawk owls, and great gray owls move southward during some winters as well.
The boreal owl ranks as one of North America’s most wanted bird species on many birders’ lists. The challenge in finding this bird is all about location, location, location. Boreal owls prefer conifer or mixed-conifer forests in an old growth northern habitat. This bird becomes even more difficult to find since it roosts in dense spruce or balsam fir conifers, five to twenty feet high, usually on a branch next to the trunk. Boreal owls are not true migrants but are irruptive in nature, with most studies showing a four to five year irruption cycle. The year 2004 was its last irruption year, with over 300 boreal owls banded on the north shore of Lake Superior in Minnesota. Small rodents such as mice and voles make up 90-98% of its diet, with insects or small birds making up for the remaining food intake. Normally a nocturnal hunter, it will also hunt during cloudy daylight hours, sitting and waiting for its prey located mostly through its hearing.
The first and only time I have observed a northern hawk owl was in the winter of 2005 at the Ashland airport, where it was spending its days on power lines or telephone poles for days before I got my first glimpse. These birds are also nomadic, wandering south of their normal northern boreal forests, again during years of high reproduction followed by low prey availability. Hawk owls are mostly diurnal (active during daylight hours,) hunting for small mammals or birds from tree top perches. These birds have also been observed caching their prey, stashing it in tree limbs for later consumption.
In the area’s snow covered fields, perched atop a telephone pole, a great gray owl can sometimes be observed. This bird’s irruptions, also believed to be related to prey availability, are perhaps more sporadic. Some great grays can be seen in our area during any winter. In Manitoba, some individuals have migrated up to 700 kilometers, compared to only 43 kilometers in Oregon. In the recent irruption year of 2004-05, over 2,000 great grays were observed in northern Minnesota, an amazing occurrence compared to the normal winter bird count of 35 of this species. One of the world’s largest owls, this bird’s five feet wingspan is an amazing sight. Its main source of food is voles and other small rodents.
Some phenologists or birders will drive great lengths to see some of these birds. If you find you are one of them, the best viewing times for great gray or northern hawk owls appear to be first thing in the morning or late afternoon. Overcast or foggy weather makes for good viewing all day. When searching, focus on tree-tops for northern hawk owls, or about eye level in areas with lots of conifers for great grays. Quality observations of these owls can happen from your vehicle, making hiking into bogs or other areas less necessary.
Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M or on the web at www.cablemuseum.org to learn more about exhibits and programs.
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